The fabrication of current all-ceramic dental restorations often requires extensive labor and time and the proficiency of highly skilled technicians. Many state-of-the-art dental restorations reveal a sense of artistry that can typically only be achieved manually or “by hand.” While aesthetics are preserved with this process, microstructural inhomogeneities may appear, affecting strength and reliability. The industry has attempted to automate this process by, for example, pressing crowns. Although pressable crowns reduce some of the skill time required, about two hours of concerted effort is necessary to complete a crown. Pressed crowns may also suffer from similar strength and reliability problems typical of “hand made” crowns.
In current practice, an impression is taken by a dentist and sent to a dental lab where a stone model is cast from the impression. A stone model is used to wax-up copings and frameworks to be invested in a refractory investment for subsequent casting or pressing. Materials used in this multi-step procedure (impression material, stone, wax, refractory investment) have their individual shrinkage/expansion characteristics adding to the “propagation” error and variability of results. Shade is taken by the dentist by comparing the patient's teeth to his shade guide and communicating this subjective evaluation to the dental laboratory. The dental laboratory fabricates the dental restoration and compares its shade to yet another shade guide. This procedure is extremely subjective and prone to error due to the inconsistencies between the shade guides.
In current automated procedures, there remain problems involving the accuracies of intra-oral scanning due to the rigorous requirements of the contact and optical digitizers, which both utilize precision immobile reference systems. Moreover, subgingival surfaces, undercuts and, very frequently, occlusal surfaces cannot be extrapolated from optical data. Therefore, even state-of-the art CAD/CAM methods (e.g., Procera®, Cercon®, Lava®, and Cerec® methods) may require casting of stone models from impressions, stones or wax models.
Devices integrating outputs from multiple sources are already in use in other areas of medicine such as combined magnetic resonance imaging (MRI) and computed axial tomography (CAT) devices. Attempts are being made to combine panoramic X-ray devices that provide accurate 3D images of jaw bones with solid-free form manufacturing machines that produce scaffolds for jaw bone reconstruction.
It would be beneficial to eliminate or reduce conventional steps used in current dentistry techniques such as the taking of impressions and the casting of models.